1. Field of the Invention
The present invention relates to an over voltage protection apparatus for use in protecting a repeater amplifier, and in particular relates to an apparatus which provides a low current path around the repeater amplifier during high voltage transients.
2. Description of the Prior Art
Prior art protection devices which are utilized to protect equipment, such as repeater amplifiers that are connected to transmission lines, attempt to absorb or bypass the high voltage surges occurring on the transmission lines by providing a shunt path to ground. The shunt path usually includes a carbon block device or a gas fired device which breaks down (conducts) when transients higher than the breakover voltage of the protection device occurs, thereby preventing the voltage surges from reaching any equipment connected to the transmission lines. Frequently, these devices include a fuseable link which shorts out the device and opens the transmission line, when high voltage transient exists for any length of time greater than can be absorbed by the protective device. This requires that the fuseable link portion, if not the whole protection device, be replaced after a high voltage transient surge is experienced.
Typical of these devices is U.S. Pat. No. 3,890,543 issued on June 17, 1975 to Gaylord D. Jonassen. Jonassen discloses a low voltage surge protection network, which includes a multi-electrode gas tube arrester having an optional integral temperature sensitive lift-off capability, wherein the multi-electrode gas tube arrester has directly across it, back-to-back zener diodes, such that voltage imbalance conditions induced across a line pair are corrected within a time interval sufficient to prevent damage to low voltage operating equipment electrically coupled across the line pair. Another device which discloses a similar type of protection is U.S. Pat. No. 4,068,277 issued Jan. 10, 1978 to Frank L. Simokat. The patent to Simokat discloses a protector, which includes a three element gas tube serially connected with a heating element, the combination being connected in shunt across the load to be protected. Between the protecting shunt path and the source, a normally closed switch is provided which is responsive to the heating element and opens in the event of sustained over voltage conditions. Accordingly, a prolonged surge which might otherwise destroy the gas tube and/or the protection load, is isolated from both the shunt protection branch and from the load, thus preventing damage to both.
Other devices known in the art provide protection by providing a narrow spark gap which breaks down (arcs over) to short the voltage surge to ground, thereby protecting the equipment. These devices, however, frequently fail in use and must be replaced, because of damage produced during the protective arcing mode. Typical of these devices is U.S. Pat. No. 4,037,266 issued on July 19, 1977 to J. H. English, et al.
Other known techniques include the combination of carbon blocks for arcing utilized together with transformers and coils to buck-out the surge voltage by inducing voltages in a series path of opposite polarity. Typical of these devices would be U.S. Pat. No. 2,338,405 issued to C. C. Cash et al on July 3, 1941. Yet another approach utilizes a zener diode configuration connected in shunt with the transmission line and a resistor attenuator pad to help absorb some of the energy once the zener diode goes into conduction. This is further backed up with a carbon block protector to absorb some of the energy of a lightning strike to the transmission line. Typical of this type of approach is disclosed in U.S. Pat. No. 3,181,033 issued to H. L. Bakker on Nov. 15, 1961. Still another approach is disclosed in U.S. Pat. No. 4,068,282 issued to F. D. Rigollet. Rigollet discloses a circuit arrangement wherein the transmission line is completely disconnected from the sending and receiving devices. The coupling between the transmission line and the sending and receiving devices includes optical coupling between the transmission line and the sending and receiving devices. With this approach a lightning strike on the transmission line would not be connected to the sending or receiving devices or repeater amplifiers which may be isolated in this manner.
Therefore, it is an object of the present invention to provide a reliable means for isolating the repeater amplifiers from high voltage transients appearing on the transmission lines coupled thereto.
It is a further object of the present invention to provide a reliable means for bypassing the voltage surges appearing on the transmission lines around a repeater amplifier utilized thereon.
It is still another object of the present invention to provide a repeater bypass protection apparatus which does not interfere with the signal appearing on the transmission line and/or repeater in normal operation, but will effectively protect the repeater apparatus during high voltage transients.
The foregoing and other objects and advantages will appear from the description to follow. In the description, reference is made to the accompanying drawing which forms a part hereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. This embodiment will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope in the present invention is best defined by the appended claims.